<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
    var count = 123;
    function fn() {
        console.log(count); //234
    }
    function fun(num) {
        console.log(count); //123
        function foo() {
            count = 234;
            console.log(count);//234
            fn();
        }
        console.log(num); //456
        foo()
    }
    fun(456)
    </script>
</body>
</html>